This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A230036 #13 Feb 16 2025 08:33:20
%S A230036 3,13,149,15377
%N A230036 Numbers n such that (39^n + 1)/40 is prime.
%C A230036 All terms are primes.
%C A230036 a(5) > 10^5.
%H A230036 J. Brillhart et al., <a href="http://dx.doi.org/10.1090/conm/022">Factorizations of b^n +- 1</a>, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
%H A230036 H. Dubner and T. Granlund, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL3/DUBNER/dubner.html">Primes of the Form (b^n+1)/(b+1)</a>, J. Integer Sequences, 3 (2000), #P00.2.7.
%H A230036 H. Lifchitz, <a href="http://www.primenumbers.net/Henri/us/MersFermus.htm">Mersenne and Fermat primes field</a>
%H A230036 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Repunit.html">Repunit</a>.
%t A230036 Do[ p=Prime[n]; If[ PrimeQ[ (39^p + 1)/40 ], Print[p] ], {n, 1, 9592} ]
%o A230036 (PARI) is(n)=ispseudoprime((39^n+1)/40) \\ _Charles R Greathouse IV_, Feb 17 2017
%Y A230036 Cf. A000978 (numbers n such that (2^n + 1)/3 is prime).
%Y A230036 Cf. A007658, A057171, A057172, A057173, A057175, A001562, A057177, A057178, A057179, A057180, A057181, A057182, A057183, A057184, A057185, A057186, A057187, A057188, A057189, A057190, A057191, A071380, A071381, A071382, A084741, A084742, A065507, A126659, A126856, A185240, A229145, A229524.
%K A230036 hard,more,nonn
%O A230036 1,1
%A A230036 _Robert Price_, Oct 05 2013